8055 ‎(2)‎

• UCREFRP Catalog Number: 8055
• Author: Crowl, T. A. and N. W. Bouwes.
• Title: A Population Model for Four Endangered Colorado River Fishes - Final Report.
• USFW Year: 1998.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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The Upper Colorado River Basin Context
We modeled the population dynamics of the four endangered fish species in the Upper
Colorado River Basin (UCRB) #o determine current patterns of population dynamics,
both temporally and spatially, as well as predictions for numbers of fish required, or
changes in demographic parameters necessary, to fulfill management targets specified
by Upper Basin researchers (see UDWR report regarding Management Objectives).
Target species included, the Colorado squawfish (Ptvchocheilus lucius), the razorback
sucker (Xyrauchen texanus), the humpback chub ( ila c ha), and the bonytail chub
(Gila eleg_ans). We began by constructing a Lotka-Volterra population model (see
model development section below) based on our general knowledge of the Upper
spatial delineation at the geomorphic reach and subpopulation scales. The original,
Basin. The model was constructed to be as specii'ic as data would allow, including,
generic model included simple demographic parameters such as fecundity, sex ratio,
and survivorship values for YOY, 1-, 2-, and 3-yr-old fish, and adults.
Following initial mode( development, a workshop was held at Utah State University to
discuss model structure, spatial components of the river itself, and subpopulations of
Colorado squawfish. Table 1 and Figure 1 represent the overall model structure
agreed to, and the geomorphic basis for the finest spatial structure ultimately used in
' the model.
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